Narrow desktop layout margins and fix taiji icon in light mode.

Cap content width at 1152px with side margins on ultrawide screens, add stroke to taiji logo for light backgrounds, and shrink backdrop watermark.

Co-authored-by: Cursor <cursoragent@cursor.com>

components/layout/mode-workspace.tsx

@@ -1,7 +1,7 @@
 "use client";
 
 import { Sparkles } from "lucide-react";
-import { APP_CONTAINER } from "@/lib/layout";
+import { MODE_CONTAINER } from "@/lib/layout";
 
 export function ModeWorkspace({
   children,
@@ -13,7 +13,7 @@ export function ModeWorkspace({
   aiTitle?: string;
 }) {
   return (
-    <div className={`${APP_CONTAINER} py-6 lg:py-8`}>
+    <div className={`${MODE_CONTAINER} py-6 lg:py-8`}>
       <div className="grid gap-6 lg:grid-cols-2 lg:items-stretch lg:gap-8 xl:gap-10">
         <div className="grid h-full min-h-0 auto-rows-fr gap-5 lg:min-h-[calc(100vh-9rem)]">
           {children}